TOXOCARIASIS: A NEGLECTED DISEASE

 

Toxocara canis and Toxocara cati are globally distributed parasitic worms that are commonly found in the digestive system of cats, dogs and foxes and can cause an infection in humans known as Toxocariasis (Schantz et al. 2008).

 

Toxocara spp. eggs are released into the environment through the infected animal’s faeces, contaminating soil (Cheprasov 2012). The eggs may also be present in a dogs coat after exposure to contaminated soil (Overgaauw & van Knapen 2004). Human toxocariasis infections are caused by ingestion of infective eggs through consumption of contaminated soil, or anything that has been in contact with contaminated soil such as unwashed vegtables.

 

Young children are considered to be most at risk due to an increased likelihood of coming into contact with contaminated soil through recreational activities (Despommier 2003). However, cases of Toxocariasis have been reported in all ages groups.

 

Public Health England recorded 30 cases of Toxocariasis in England and Wales between 2000 and 2010. However, this number may not accurately reflect the true number of Toxocariasis cases as the condition can produce no symptoms (asymptomatic infections) and can often be misdiagnosed. 

 

Toxocara spp. egg found in soil
Toxocara spp. egg found in soil

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Toxocara spp. egg found in soil
Toxocara spp. egg found in soil

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THE SCIENCE BEHIND BARC 

BARC is attempting to determine the distribution of common soil parasites around the UK. Among the parasites that BARC is interested in are Toxocara canis and Toxocara cati, nematode roundworms that have the ability to infect animals and humans. The information below demonstrates why determining the prevalence of Toxocara spp. in the UK is important and why it is crucial for increasing public understanding of dog fouling and its links to human disease.

TOXOCARIASIS IN DOGS 

 

 

In 2014, 24% of UK homes owned at least one pet dog (Pet Food Manufacturers Association) and most will be infected with Toxocara spp. at some point in their lives (Overgaauw & van Knapen  2013). Thus, dogs pose a threat to humans in terms of Toxocariasis. 

 

Like humans, dogs acquire Toxocara infection through ingestion of infective Toxocara spp. eggs. The Toxocara spp. larvae then hatch from the eggs and migrate throughout the blood stream and tissues of the dog. Migration can either end in the intestine where the worms breed and produce eggs that will be released in faeces, or in other tissues where the larvae can form dormant cysts. 

 

These dormant cysts play an important role in transmission of Toxocara spp. from bitches to their puppies. Puppies younger than six months  tend to have the highest Toxocara spp. worm burdens (Overgaauw & van Knapen  2013) due to activation and migration of the larvae from the tissues of the bitch to the puppies before they are born (Transplacental Transmission). Toxocara spp. infection can also be transmitted to puppies after they are born through the milk of their infected mother (Lactogenic Transmission). 

 

Frequently de-worming dogs, such as Mollie, is a simple step taken to try and limit environmental contamination with Toxocara spp. eggs. However, de-worming has to be an on-going control method as dogs may become reinfected shortly after treatment.